Using worms to study brain function
The worm C. elegans constitutes a good model for studying the nervous system even though it only consists of 302 neurons. Despite that simplicity, worms can sense and respond to various sensory stimuli including taste, odour, temperature, ultraviolet (UV) light and mechanical stimuli. Additionally, the ease of genetic manipulation coupled to the huge repository of mutants allows thorough examination of the roles of various genes in the nervous system. Using C. elegans as a model, the EU-funded Ytanizawa project studied the interaction of sensory stimuli in the nervous system. In order to characterise arousal regulation by external sensory cues, scientists applied various stimuli to animals and quantified their behavioural change. More specifically, they applied a combination of mechanical stimuli to the body and artificial activation of nociceptive neurons with light-gated ion channel channelrhodopsin-2, and analysed the withdrawal response of worms. Results showed no sign of additive effect when the two inputs were presented simultaneously. However, when they were given consecutively, an enhanced response to the second stimulus was observed accompanied by increased motor activity. By screening available mutants, project members also found that neuropeptide signalling played a role in such arousal modulation. Ytanizawa results contributed significant insight into the mechanism of arousal modulation and proved the usefulness of C. elegans in studying multisensory processing, ranging from gene to behaviour. Understanding how arousal modulation is regulated at the cellular level could possibly identify multisensory integration effects and provide knowledge access to a highly inaccessible system such as the brain.
